Drains
Leaking drains and subsidence
Leaking drains cause most subsidence in Irish houses. Estates built before the 1980s, before uPVC drains, usually have clay sewers: short pipes pushed together with no rubber seal, and a leak at one joint washes the ground out from under the foundations. In Census 2022, 28.5% of Irish homes were built before 1971.
Caught early, the fix can be new drains alone. Left, the ground under the walls loses its strength and underpinning follows.
Free, no obligation. One local contractor talks it through, not five.
How do leaking drains cause subsidence?
A slight leak at one joint softens the ground under it. The pipe slips, the next joint opens, and the cycle carries on until the ground beside the foundations has lost much of its strength. The wall above it drops a little, unevenly, and cracks.
How do I know if my drains are clay?
- The house is in an estate or suburb built in the early 1970s or before
- Manhole covers and gully heads aren't plastic
- Lift a manhole cover: brown or orange glazed pipe in short lengths is clay
- The drains have never been replaced
Clay drains that aren't leaking now will eventually leak.
What are the signs the drains are the cause?
- Cracks near where the drains run, often at the back of the house or by the kitchen and bathroom
- Diagonal cracks from the corners of windows and doors
- Blocked or slow drains alongside the cracking
- A gully or manhole that keeps flooding
- Paving or ground sinking over the drain run
How are the drains checked?
With a CCTV survey: a camera goes down the pipes and shows cracks, open joints, roots and collapses, with a map of where the drains run. It's the first thing an engineer asks for when a house has cracks. See our price guide for typical costs.
What does the repair involve?
- Dig out the old clay drains and the affected soil.Back to sound ground.
- Stabilise the ground under the foundations.By underpinning or injection, if the engineer's design calls for it.
- Lay new uPVC drains on drainage aggregate.Sealed joints, then tested before they're covered.
- Reinstate the ground.Paths, patio and garden made good.
- Repair the cracks later.Six months to a year on, once movement has stopped.
Can new drains fix it without underpinning?
Sometimes. If the leak is caught before the ground under the walls has lost much strength, replacing the drains may be enough. The longer it's left, the bigger and dearer the repair. The engineer decides. See when underpinning isn't needed.
Will insurance pay?
Subsidence from a leaking drain can be an insured event. Tell the insurer as soon as reasonably possible and give full details within 30 days. A subsidence excess applies, and damage that started before the policy is excluded. See subsidence insurance.
Start with a chartered structural engineer. Nobody can tell from a photo or a phone call whether a house needs underpinning. An engineer looks at the cracks, the ground and the drains, then decides. This site never tells anyone their house is safe or unsafe.
FAQ
Questions people ask
Can a leaking drain really crack a house?
Yes. It's the most common cause of subsidence in Irish houses. Water from an open joint softens and washes away the ground under the foundations.
Are uPVC drains safe from this?
uPVC drains have sealed joints, so they don't leak the way old clay socket pipes do. Clay drains came before uPVC, in houses built before the 1980s.
Should I replace clay drains before cracks appear?
If a CCTV survey shows open joints or cracked pipes, fixing them early is the cheaper repair. Clay drains that aren't leaking now will eventually leak.
Do I need underpinning if I replace the drains?
Not always. The engineer decides from the cracks and the ground. Caught early, new drains can be enough.
Who will ring me?
We pass your request to one experienced groundworks and underpinning contractor who covers your county. Your number isn't sent to a list. They ring you, ask what's happening and about any engineer's report, and price the work from the engineer's design. Nothing is booked until you say yes.
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